It is a problem in the field of cellular communications to efficiently and continuously meet the communications requirements of the passengers in multiple aircraft as the aircraft fly their routes and approach/depart airports.
A typical Air-To-Ground cellular communications network (including the Ground-To-Air link) consists of a number of terrestrial (ground) base stations, each of which provides a radio frequency coverage area in a predetermined volume of space, radially arranged around the cell site transmitting antenna. This terrestrial base station uses an antenna pattern which is insensitive to the reception of ground-originating or ground-reflected signals and which antenna pattern is transmissive only in a skyward direction. The terrestrial base stations are geographically distributed, generally following a typical cellular communications network layout. Terrestrial base stations can also be co-located near airports to enable network coverage when aircraft are on the ground; in this case, the antenna patterns are optimized for terrestrially located aircraft. The boundaries of the coverage area of each terrestrial base station are substantially contiguous with that of neighboring sites so that the composite coverage of all of the terrestrial base stations in the Air-To-Ground cellular communications network generally provides coverage over the targeted area. Terrestrial base stations may provide either a single omni cell of coverage using transceiver(s) associated with a single transmit and receive antenna system or multiple sectors within the cell of coverage, each with associated transceivers and the associated transmit and receive antennas. The advantage of the latter arrangement, with multiple sectors per terrestrial base station, is to allow provision of increased call handling capacity in the coverage area of that terrestrial base station.
There are limitations on the total radio frequency spectrum available and, therefore, limitations on the total available call handling capacity in any single cell. As a wireless communications device moves from the coverage area of one cell or a cell's sector into the coverage area of a spatially contiguous adjacent cell or cell's sector, the communications from that wireless communications device are handed over from the first cell (or first sector) to the second cell (or second sector). This requires that there be adequate available call handling capacity in the second cell to support the new load represented by this wireless communications device. Call handoffs that entail a single personal wireless communications device do not create large transient loads on a cell. However, in an Air-To-Ground cellular communications network, the number of presently active cellular calls within an aircraft may represent a large fraction of the call handling capacity of a terrestrial cell site since each aircraft may have hundreds of passengers, each vying for network capacity. With the small number of aircraft that can be served by a cell site and long average transit times for aircraft within a cell, there must be a large allowance of idle capacity to serve aircraft which may arrive before the presently served aircraft leave the cell and free up call handling capacity within the cell. In addition, the use of the single radio frequency link between the aircraft and the serving terrestrial cell site represents a single point of failure, where a service interruption impacts a multitude of calls.
Thus, the radio frequency communications link between the aircraft and the terrestrial base stations of the Air-To-Ground cellular communications network has limited capacity, represents a single point of failure, and represents a call handoff problem in terms of call handling capacity of the serving terrestrial cell sites.
What is needed is an advance in the art which solves the Air-To-Ground cellular communications network call handling capacity problem and dramatically improves system availability, system reliability, and system capacity.